THE Intergovernmental Panel on Climate Change’s (IPCC) Impacts volume of the Fifth Assessment Report will be released today. Here, three contributors to the health chapter explain the ideas and evidence behind the report.

The consequences of human-driven global climate change as this century progresses will be wide-ranging. Yet public discussion has focused narrowly on a largely spurious debate about the basic science and on the risks to property, iconic species and ecosystems, jobs, the GDP and the economics of taking action versus taking our chances.

Missing from the discussion is the threat climate change poses to Earth’s life-support system – from declines in regional food yields, freshwater shortage, damage to settlements from extreme weather events and loss of habitable, especially coastal, land. The list goes on: changes in infectious disease patterns and the mental health consequences of trauma, loss, displacement and resource conflict.

In short, human-driven climate change poses a great threat, unprecedented in type and scale, to well-being, health and perhaps even to human survival.

The human health chapter in the second (“Impacts”) volume of the IPCC’s Fifth Assessment Report concludes that the scientific evidence of many current and future risks to health has strengthened in recent years. The chapter, as in all IPCC reports, reviews all existing scientific evidence and is subject to external peer-review.

During at least the next few decades, the chapter states, climate change will mainly affect human health, disease and death by exacerbating pre-existing health problems. The largest impacts will occur in poorer and vulnerable populations and communities where climate-sensitive illnesses such as under-nutrition and diarrhoeal disease are already high – thus widening further the world’s health disparities.

Currently, the worldwide burden of ill-health clearly attributable to climate change is relatively small compared with other major blights on health such as from poverty, poor sanitation and exposure to tobacco.

Even so, in this early stage of human-driven climate change researchers in many countries have reported that rising temperatures and changing rainfall patterns have, variously, increased heat-related illnesses and deaths, altered the distribution of some water-borne infectious diseases and the insect transmitters (vectors) of some diseases (such as malaria), and have reduced food yields in some already food-insecure populations.

Less certainly, extreme weather events, influenced in part by climate change, are likely to have contributed to the recent rise in global food prices.

The chapter discusses three impact categories in particular:

under-nutrition and impaired child development due to reduced food yields

injuries, hospitalisations and deaths due to intense heat waves, fires and other weather disasters and

shifts in the seasonal duration and spatial range of infectious diseases.

There is also mounting evidence of the adverse health consequences of workplace exposure to heat extremes, including reduced work capacity and productivity.

Looking ahead to 2100, for which some modelled scenarios now project an average global warming of 4 degrees Celsius, the report foresees that in such conditions people won’t be able to cope, let alone work productively, in the hottest parts of the year. And that’s assuming social and economic institutions and processes are still intact. Some regions may become uninhabitable.

Impacts on mental health could be similarly extreme, further limiting our collective capacity to cope, recover and adapt.

Overall, while limited health gains from climate change may occur in some regions, the health chapter concludes from the evidence that harmful impacts will greatly outweigh benefits. The impacts of climate change will also undermine hard-won gains achieved through social development programs, impeding progress in the world’s poorest countries.

The world community has dithered for two decades over climate change since it rose to prominence during the 1992 Earth Summit. As valuable time to reduce the risks (mitigation) has been squandered, the need to also focus on managing risk (adaptation) has increased. But excessive reliance on adaptation carries its own risks – including fooling ourselves that we don’t need immediate and aggressive mitigation.

The health chapter concludes that the most immediate effective way to manage health risks is through programs that introduce or improve basic public health measures. It also notes the need to boost human rights-based access to family planning.

As climate change proceeds, additional climate-specific measures (such as enhanced surveillance, early warning systems and climate-proofed building design) will be needed to protect population health, even in high-income settings. Recent extreme events such as the severe heat waves and fires in Australia in 2009-2014 and in Russia in 2010 underscore this need.

The chapter offers some cheer in stressing that the near-term and relatively localised health “co-benefits” from reducing greenhouse emissions (mitigation) could be very large. Reducing emissions of methane and black carbon, for example, may avoid more than two million deaths per year.

encouraging communities to be more active via improved public transport and reduced car reliance

reducing exposures to temperature extremes with well-insulated energy-efficient housing and

promoting healthier diets through the transformation of food production and processing systems.

In economic terms, the IPCC chapter judges that the health co-benefits from reducing emissions would be extremely cost-beneficial. They would, for example, be one thousand times greater than the economic co-benefits to agricultural yields from reduced exposures to short-lived, crop-damaging, airborne climate pollutants.

Overall, the up-front costs of reducing emissions could be substantially offset by early and extremely large health (and other) benefits.

Of course, none of this matters if human well-being, health and survival mean little to us. In that case we can emit all we like, then suffer, dwindle or even die out as a species and leave this planet to recover and thrive without us. One way or another we will then emit less.

We have a closing window of time in which to do something about global climate change.

Anthony McMichael receives funding from The National Health and Medical Research Council. He is affiliated with The Climate Institute.

Colin Butler receives funding from the Australian Research Council. He is co-director of the NGO Benevolent Organisation for Development, Health and Insight.

Helen Louise Berry receives funding from the National Health and Medical Research Council and the Australian Research Council. She is a member of the Australian Labor Party.